Tag: SSTR-PET

When I was offered my very first Ga68 PET/CT at a 6 monthly surveillance meeting in May 2018, I was both excited and apprehensive. Let me explain below why I had a mix of emotions.

I was diagnosed in 2010 with metastatic NETs clearly showing on CT scan, the staging was confirmed via an Octreotide Scan which in addition pointed out two further deposits above the diaphragm (one of which has since been dealt with). In addition to routine surveillance via CT scan, I had two further Octreotide Scans in 2011 and 2013 following 3 surgeries, these confirmed the surveillance CT findings of remnant disease. The third scan in 2013 highlighted an additional lesion in my thyroid (still under a watch and wait regime, biopsy inconclusive but read on….).

To date, my 6 monthly CT scans seem to have been adequate surveillancecover and all my tumour and hormone markers remain normal. I’m reasonably fit and well for a 62-year-old.

Then I ventured into the unknown

this is not actually my scan!

I wrote a comprehensive post about the Ga68 PET entitled “…. Into the unknown” – so named because that is how I felt at the time. It’s well-known that the Ga68 is a far superior nuclear scan to the elderly Octreotide type, showing much greater detail with the advantage of providing better predictions of PRRT success if required downstream. It has been a game changer for many and if you look below and inside my article, you will see statistics indicating just how it can ‘change the game’ in somatostatin receptor positive Neuroendocrine Cancer diagnostics and treatment.

The excitement of the Ga68 PET

I was going to get the latest ‘tech’ and thought it could be useful confirmation of what I already knew. I also felt lucky to get one, they are limited in UK and there has to be a clinical need to get access. I was excited because it might just rubber stamp the stability I’ve enjoyed for the past 5 or so years since my last surgery in 2012.

The apprehension of the Ga68 PET

I also felt apprehensive because of the ‘unknown’ factor with cancer, i.e. what is there lurking in my body that no-one knows about, and which might never harm me but this scan will light it up demanding attention. I was also apprehensive in case this more detailed scan found something potentially dangerous. As we know, NETs are mostly slow-growing but always sneaky. Of course, any new tumours found may not actually be new, they were just not seen until the Ga68 PET was able to uncover them. How annoying!

Is the Ga68 PET Scan a game changer?

To confirm the advantages of SSTR PET over Octreotide scans, a study comprising 1,561 patients reported a change in tumour management occurred in over a third of patients after SSTR PET/CT even when performed after an Octreotide scan.

In 4 of 14 studies, SSTR PET/CT was performed after an 111In-Octreotide scan. In this subgroup, additional information by SSTR PET/CT led to a change in management in 39% (range, 16%-71%) of patients.

Seven of 14 studies differentiated between inter- and intramodality changes, with most changes being intermodality (77%); intramodality, (23%). (note: intermodality means changes within the same treatment, intramodality means change to another treatment).

In an older study, this slide from a NET Research Foundation conference shows some more interesting statistics:

This slide from a recent NET Research Foundation conference confirms the power of more detailed scanning

Was Ga68 PET a game changer for me?

Yes, I believe so. I’m now in the ‘bone met club’ and although that single metastasis has probably been there for some time, it’s not a ‘label‘ I was keen to add to my portfolio. If I was to be 100% honest, I’m not totally convinced it’s a metastasis. The scan has brought more light onto my thyroid issue. In fact it indicates even more potential issues above the diaphragm including what looks like a new sighting around my left pectoral lymph nodes. The scan also lghts up a known issue in the left clavicle lymph nodes, first pointed out via Octreotide scan in 2010 and biopsy negative.

In addition to a nuclear scan update (routine surveillance), it also formed part of an investigation into progression of my retroperitoneal fibrosis (initially diagnosed 2010 but potential growth spotted on recent surveillance CT). The Ga68 PET doesn’t make fibrosis light up (it’s not cancerous) but there are some hotspots in the area of the aorta close to the fibrosis, a potential source if the cause. Surgery is on hold for now as my kidney function is fine following a renal MAG3 scan which reported no blockages.

It would appear I’m no longer a boring stable patient

The Ga68 PET Scan confirmed:

Bone Metastases. Report indicates “intense focal uptake“. It always amazes me that people can be thankful for having an extra tumour. I’m thankful I only have a single bone metastasis (right rib number 11). I had read so many stories of those who got their first Ga68 PET and came back with multiple bone metastases. I’ll accept one and add to my NET CV. I have no symptoms of this bone metastasis and it will now be monitored going forward. I’m annoyed that I don’t know how long it’s been there though!

Left Supraclavicular Fossa (SCF) Nodes lighting up “intense uptake“. I’ve had an exploratory biopsy of the SCF nodes, 5 nodes removed negative. Nothing is ‘pathologically enlarged’ in this area. Monitored every 6 months on CT, annually on ultrasound. I had 9 nodes removed from the left axillary in 2012, 5 tested positive for NETs and this area did not light up. This whole area on the left above the diaphragm continues to be controversial. My surgeon once said I had an unusual disposition of tumours. (Edit: Nothing sinister or worryingly enlarged showing on Jan 2019 ultrasound – measuring 6mm).

Report also highlights left subpectoral lymph nodes which is new. The subpectoral area is very interesting as from my quick research, they are closer to the left axillary (armpit) nodes than they are to the SCF nodes. I’m hoping to get an ultrasound of these in January at my annual thyroid clinic (Edit: nothing sinister showing on ultrasound in Jan 2019).

My known liver metastases lit up (remnant from liver surgery 2011) – not marked as intense though. The figure of 3 seems to figure highly throughout my surveillance scans although the PET report said “multiple” and predominately right-sided which fits.

Retroperitoneal area. This has been a problem area for me since diagnosis and some lymph nodes are identified (intense word not used). This area has been highlighted on my 3 octreotide scans to date and was first highlighted in my diagnosis trigger scan due to fibrosis (desmoplasia) which was surrounding the aorta and inferior venous cava, some pretty important blood vessels. I wrote an article on the issue very recently – you can read by clicking here. So this scan confirms there are potentially active lymph nodes in this area, perhaps contributing to further growth of the fibrosis threatening important vessels – read below.

I have learned so much about desmoplasia since this issue arose that I now fully understand why I had to have radical surgery back in 2010 to try to remove as much of the fibrosis as possible from the aortic area. You can read more about this in my article. Desmoplasia via fibrosis is still very much of an unknown and mystery condition in NETs.

I now know that my fibrosis is classed as clinically significant and according to the Uppsala study of over 800 patients inside my article, I’m in 5% of those affected in this way (2% if you calculate it using just the retroperitoneal area).

It appears this problem has come back with new fibrosis or growth of existing fibrosis threatening to impinge on blood vessels related to the kidneys and also my ureters (kidney to bladder urine flow). The Ga68 PET doesn’t make fibrosis light up (it’s not cancerous) but there are some hotspots in the area of the aorta close to the fibrosis.

I didn’t expect this particular problem to return – it was a bit of a shock. My hormone markers have been normal since 2011 and this just emphasises the importance of scans in surveillance.

Conventional Imaging is still important though

There’s still quite a lot of hype surrounding the Ga68 PET scan and I get this. However, it does not replace conventional imaging (CI) such as CT and MRI scans which still have their place in routine surveillance and also in diagnostics where they are normally at least the trigger for ‘something is wrong’. For the vast majority, a CT/MRI scan will find tumours and be able to measure reductions and progress in regular surveillance regimes. In fact, the retroperitoneal fibrosishas appeared on every CT scan since diagnosis but the changes were highlighted on my most recent standalone CT and it triggered the Ga68 PET (although my new Oncologist did say I was due a revised nuclear scan). It’s not a ‘functional’ issue (although it is caused by functional tumours). In fact the fibrosis is not mentioned on the Ga68 PET because it is not lighting up – but the lymph nodes surrounding it are mentioned and they are under suspicious as being active.

There are actually recommended usages for the Ga68 PET scan here. For example, it is not recommended for routine surveillance in place of CI.

Scans – ‘horses for courses’

Read a summary of all conventional scans and nuclear scans by clicking here.

Next Steps

I had a meeting with my Oncologist and Surgeon and a surgical plan is possible in the event of a problem. My surgeon explained it all in his wonderfully articulate and brilliant surgical mind. Fortunately it’s not really urgent but pre-emptive treatment may be required at some point as the consequences of kidney/bladder function are quite severe. Following some further checks, the anticipated surgery is on hold for now as my kidney function is fine following a renal MAG3 scan which reported no blockages. I continue to have monthly renal blood tests and it was hinted another renal MAG3 could be done at the end of the year.

Summary

My game has changed, that’s for sure. I’m now entering a new phase and I’m waiting on details of my revised surveillance regime. However, at least my medical team and I now know what WE are dealing with and the risks vs benefits are currently being assessed. I’m heavily involved in that.

Cancer is a growth industry …literally! More people are being diagnosed than ever before. Fortunately, more people are surviving than ever before. This is against a backdrop of better awareness, better screening in the big population cancers, and to a certain extent better diagnostic tools, all of which is leading to earlier diagnosis.

So how does this affect Neuroendocrine Cancer?

According to the latest SEER database figures for Neuroendocrine Cancer, one reason for the 7 fold increase in incidence rates since the 1970s is all of those things above including better diagnostics. This has led to a revised set of epidemiological information in many countries that have made the effort to accurately update their cancer registries and there are consistent reports of incidence rates way beyond the recognised rare thresholds. Another piece of good news is that the increase in NET incidence is also due to earlier diagnosis. To sum that up – NETs is also a growth industry.

Better diagnostics

Combined with more awareness and education (including the important pathologists), more NETs than ever are being found, and many found earlier. However, it’s not party time yet because there remains far too many misdiagnoses due to the low population of the disease and the difficulty in diagnosing it. I want to focus on scanning (thus the title of the article). Whilst there are really important factors involved in a diagnosis, such as tumor and hormone markers, and biopsies (tissue is the issue), a scan is very frequently what triggers many deeper investigations to unearth a NET, i.e. if you can see it, you can normally detect it (whatever the ‘it’ is). And I include the widespread availability and increasing advances in endoscopy/ultrasounds/cameras which have also been instrumental in picking up many Gastrointestinal NETs.

The Gallium 68 PET Scan

There’s a lot of excitement about the Gallium 68 PET Scan since it was approved by the US FDA. It’s not new though and has been in use in several countries for some time. It’s a ‘nuclear scan’ and can often form part of what is known as a ‘Theranostic Pair’ (i.e. in conjunction with a therapy – read more here).

What does it do?

It comprises two main components – a PET scanning machine, and the use of a diagnostic imaging agent which is injected into the person undergoing the scan. Most machines have an inbuilt CT which forms part of the scan. The agent is a somatostatin analogue labeled radionuclide (Gallium 68) and basically the PET will then be used to see where the peptide/radionuclide mix ‘loiters’ (i.e. where there are concentrations of somatostatin receptors (SSTR) normally indicating ‘focal intense abnormality‘ of the type that is regularly found with NETs.

Imaging Agents. There are different agent variants, namely, DOTATATE, DOTATOC and DOTANOC. In USA, you may sometimes see this referred as NETSPOT which is more of a commercial label for the agent (NETSPOT is a DOTATATE). Ga68 PET or SSTR PET are common descriptors for the entire process regardless of the compound. Clearly the scan works best for those with ‘somatostatin receptor positive’ tumours.

These newer agents have several benefits over the elderly In111-pentetreotide (Octreotide scan), including improved detection sensitivity, improved patient convenience due to the 2-3 hour length of the study (compared to 2 or 3 days with Octreoscan), decreased radiation dose, decreased biliary excretion due to earlier imaging after radiotracer administration, and the ability to quantify uptake. The quantification of the uptake can help decide whether a patient is suitable for radionuclide therapy such as PRRT. Eventually, all Octreotide scans should be replaced with SSTR PET but it will take some time (and money).

Octreoscan vs Ga68 PET

To confirm the advantages of SSTR PET over Octreotide scans, a study comprising 1,561 patients reported a change in tumour management occurred in over a third of patients after SSTR PET/CT even when performed after an Octreotide scan. Worth pointing out that SSTR PET is replacing the ageing Octreotide scan and not conventional imaging (CI). You can see the recommended scenarios for use of SSTR PET in this article published by the Journal of Nuclear Medicine. The slide below is interesting, although it was a small study. However, you can see the treatment changes as a result of a Ga68 PET are quite striking.

This slide from a NET Research Foundation conference confirms the power of more detailed scanning

I see many people complaining because the cannot get access to a Ga68 PET which is available through their healthcare system or local hospital. Many of these issues are insurance based. Worth pointing out that there are actually recommended usages for the Ga68 PET scan here. For example, it is not recommended for routine surveillance in place of Conventional Imaging (CI).

Any pitfalls with Ga68 PET Scan?

When you look at the study data above, it looks like an excellent addition to the diagnostic and surveillance toolkit for NETs. However, one of the challenges with modern scanning equipment and techniques is the ability to correctly interpret the results – in my opinion, this is almost as important as the efficiency of the machines and radionuclides. This requirement has been acknowledged in many articles and I particularly like this technical paper from a very experienced nuclear medicine physician Professor Michael Hofman from the Centre for Cancer Imaging at the Peter MacCallum Cancer in Melbourne. I had a chat with Professor Hofman who added that this is a very sensitive scan, so often picks up “new” disease, which isn’t really new, just never identifiable on standard imaging. However, there’s an excellent section on pitfalls in interpretation and I’m quoting an abstract below.

“Although GaTate PET/CT is a highly sensitive and specific technique for NETs, the attending physician or radiologist must be aware of various physiologic and other pathologic processes in which cellular expression of SSTR can result in interpretative error. Most of these processes demonstrate low-intensity and/or nonfocal uptake, in contrast with the focal intense abnormality encountered in NETs. Causes of interpretative pitfalls include prominent pancreatic uncinate process activity, inflammation, osteoblastic activity (degenerative bone disease, fracture, vertebral hemangioma), splenunculi or splenosis, and benign meningioma.”

“The highest-intensity physiologic uptake of GaTate is seen in the spleen, followed by the adrenal glands, kidneys, and pituitary gland”

It follows that failure to interpret nuclear scans alongside the patient’s clinical history can sometimes result in two big issues for patients:

1. Unnecessary worry when ‘something’ shows up which is actually a false positive.

2. Something which leads to irreversible treatment when it is was not required.

Just imagine something which is 40 times better than current PET scan technology? That’s what the scientists are working on now. Here’s an example called “EXPLORER“. You can update yourself here. The issue of interpretation will be even more difficult when the new generation of scans appear. There’s an excellent article from Cancer Research UK talking about the modern phenomenon called ‘overdiagnosis’ – readhere

Lanreotide and Octreotide and timing the scan?

From the same technical document referred above, here’s an extract (updated to include Lanreotide). “Uptake at physiologic and pathologic sites may change in patients who undergo concomitant short- or long-acting somatostatin analog therapy, which competes with the radiotracer for bioavailability. We generally discontinue short-acting octreotide for 12–24 hours and perform imaging in the week before the next dose of long-acting Octreotide/*Lanreotide, which is typically administered monthly“. It’s actually the same text as found in the manufacturer’s drug leaflet (click here). More evidence behind the reason for this restriction is found here (please refer to the comments on Ga68 PET – the article also covers the issue of PRRT which is very interesting as a separate subject to the scan timings).

*added by the author for completeness.

Having my first Ga68 PET Scan after 8 years of living with NETs?

When I was offered my very first Ga68 PET/CT at my recent 6 monthly surveillance meeting, I was both excited and apprehensive. I was diagnosed in 2010 and my staging was confirmed via an Octreotide Scan pointing out two further deposits (one of which has since been dealt with). I’ve had two further Octreotide Scans in 2011 and 2013 following 3 surgeries. The third scan in 2013 highlighted my thyroid lesion – still under a watch and wait regime. So far, my 6 monthly CT scans seemed to be adequate surveillance cover and my markers remain normal.

I’m apprehensive because of the ‘unknown’ factor with cancer – what is there lurking in my body that no-one knows about and which might never harm me.

I’m excited because it might just confirm that there is nothing new to worry about.

However, I’m both excited (morbidly) and apprehensive because the scan might find something potentially dangerous. As we know, NETs are mostly slow growing but always sneaky. That said, at least I will know and my medical team will know and be able to assess the risk and decide on a course of action.

Doing the Scan

On 5th June 2018, I attended a very experienced Ga68 PET establishment called Guys Cancer Centre in London. I arrived and was immediately taken under the wing of the nuclear medicine guys who asked me fairly in depth questions about my clinical background. They then inserted a cannula ready for the injection of the radiolabelled tracer. I was then installed in the ‘hot room’ where they injected the radionuclide tracer through the cannula and then I had to remain in the hot room for 1 hour to let the tracer circulate. After 1 hour, I was taken to the PET scanner and it took around 30-35 minutes. Following that I was allowed to leave for home. It was an extremely easy experience and a significant improvement on doing the 3 day Octreotide scan.

NANETS (North American Neuroendocrine Tumor Society) is one of the biggest NET conferences, bringing together NET Specialists from around the world to discuss state-of-the-art treatment modalities, new therapies, and ongoing controversies in the field of Neuroendocrine Neoplasms (Tumors and Carcinomas). This is fairly complex stuff but much of it will be familiar to many. I’ve filtered out several outputs from the conference which I think are both relevant and topical to patients. The list is below allowing you to easily peruse and read further via linkages if you need to read more. Remember, some of these are extracts so do not contain all the details of the research or study – although some of the linkages will take you to in-depth information if that’s your bag. Where applicable, I’ve also linked to some of my blog posts to add context and detail in patient speak. The list comprises articles which were published in medical news media and for which I received alerts. It does not comprise the entire schedule of NANETS 2017. I may add more to the list if other relevant and interesting articles are published downstream.

Please note:Some of the output from the conference is in ‘study form’ and has not yet been published as peer-reviewed data (important notice to readers).

NANETS to Bring All Specialties in the NETs Community Together for 10th Annual Symposium

Scanning is a key diagnostic support and surveillance tool for any cancer. Even though you have elevated bloods or urine (….or not), a picture of your insides is really like a thousand words…. and each picture has a story behind it. Scanning can be a game changer in the hunt for tumours and although scans do not normally confirm the cancer type and grade, they certainly help with that piece of detective work and are key in the staging of the cancer.

When I read stories of people in a difficult diagnosis, I always find myself saying ‘a scan might resolve this’ and I always suggest people should try to get one. Even in the case of a story about late diagnosis or a misdiagnosis, I find myself thinking ‘if only they had done a scan earlier’. Despite what you read on NET forums, a CT scan will be able to find some evidence of tumour activity in 90-95% of cases. However, some are cunningly small or hiding and it can be like trying to find a needle in a haystack.

However, scans are not an exact science…..not yet! Apart from human error, sometimes tumours are too small to see and/or there are issues with ‘pickup’ (i.e. with NETs, nuclear scans need efficient somatostatin receptors). The differences between scan types are more quality (sensitivity) related as new technologies are introduced.

As for my own experience, I was very lucky. I managed to get a referral to a specialist early on in my diagnosis phase. He looked at the referral notes and said “what are you doing this afternoon“. I replied “whatever you want me to do“. He didn’t know I had cancer but his instincts led him to believe he needed to see inside my body, he wanted to scan me. The scan results were pretty clear – I had a metastatic Cancer and further checks were now needed to ascertain exactly what it was. So I took my seat on the roller coaster. Medicine is not an exact science (not yet anyway) but here’s something I believe is a very common occurrence in all cancers – If your doctors don’t suspect something, they won’t detect anything.

There’s frequent discussion about the best types of scans for different types of NETs and which is best for different parts of the anatomy. There’s also different views on the subject (including in the medical community), However, a few well known facts can be gleaned from authoritative NET sources:

Conventional Imaging

Computed Topography (CT)

CT scans are often the initial imaging study for a patient presenting with signs or symptoms suggestive of many cancers including NET. These studies are most useful for disease staging and surgical planning as they provide excellent anatomic detail of the tumors themselves and surrounding structures. Primary NETs (GI and lung NETs) and their metastases are generally hyperenhancing with IV contrast and are best seen in the arterial phase of a triple phase CT scan.

In primary NETs, the average sensitivity of a CT scan is 73%. CT scans have even better sensitivity in detecting NET metastases, as they demonstrate 80% sensitivity for liver metastases (but see MRI below) and 75% sensitivity for other metastases (non-liver). This modality is also useful when the primary tumor site is unknown. In one single-institution retrospective study, it was the most common study ordered to look for an unknown primary tumor site and was able to uncover the primary in 95% of cases.

Magnetic resonance imaging (MRI)

MRI is the best conventional study to detail liver metastases in NETs. It is not as useful as CT for the detection of primary small bowel lesions or their associated lymphadenopathy, but is good for the detection of primary pancreatic NETs. A study comparing MRI, CT and standard somatostatin receptor-based imaging (OctreoScan) reported 95.2% sensitivity for MRI, 78.5% sensitivity for CT and 49.3% sensitivity for the OctreoScan in detecting hepatic metastases. MRI also detected significantly more liver lesions than the other two modalities.

You may see something called Magnetic Resonance Cholangiopancreatography (MRCP). Magnetic resonance cholangiopancreatography (MRCP) is a special type of magnetic resonance imaging (MRI) exam that produces detailed images of the hepatobiliary and pancreatic systems, including the liver, gallbladder, bile ducts, pancreas and pancreatic duct.

Ultrasound (US)

The primary role of conventional ultrasound in neuroendocrine disease is detection of liver metastases and estimation of total liver tumor burden. This technique has the advantages of near-universal availability, intraoperative utility, minimal expense and lack of radiation. Most examinations are performed without contrast, which limits their sensitivity (compared with CT and MRI). I know in my own situation, US was used as a quick check following identification of multiple liver metastasis during a CT scan. I’ve also had US used to monitor distant lymph nodes in the neck area but always in conjunction with the most recent CT scan output.

Endoscopic Ultrasound (EUS)

With increased access to endoscopy, NETs in the stomach, duodenum, and rectum are increasingly incidentally detected on upper endoscopy and colonoscopy. Patients are frequently asymptomatic without any symptoms referable to the a NET (i.e. non-functional). EUS has also been used to survey patients at increased risk of developing pancreatic NETs. For example, patients with multiple endocrine neoplasia (MEN). They are also frequently used in conjunction with biopsies using fine needle aspiration (FNA) guided by EUS.

18FDG PET

18-Fluoro-Deoxy-Glucose PET (FDG PET) is used to detect malignancy for a variety of tumor types. Unfortunately, its utility has not been borne out in NETs, as the majority of NETs tend to be relatively metabolically inactive and fail to take up the tracer well. However, high-grade NETs are more likely to demonstrate avid uptake of 18FDG, giving these scans utility in identifying tumors likely to display more aggressive behavior.

18F-FDOPA PET

The use of Fluoro-18-L-Dihydroxyphenylalanine (18F-FDOPA) in PET was developed in the 80’s for the visualisation of the dopaminergic system in patients with degenerative disorders, such as Parkinson’s Disease and related disorders. The ﬁrst publication on the use of 18F-FDOPA PET for brain imaging was in 1983, which was followed by many others on the use of 18F-FDOPA PET for the diagnosis of Parkinson’s disease. Years later, in 1999 the ﬁrst publication on the use of 18F-FDOPA PET for imaging of neuroendocrine tumour appeared. The value of 18F-FDOPA PET has now been proven for the diagnosis and staging of many neuroendocrine tumours, brain tumours and congenital hyperinsulinaemia of infants.

18F-FDOPA is accurate for studying well differentiated tumours. However the difficult and expensive synthesis have limited its clinical employment. It currently can be successfully used for imaging tumours with variable to low expression of somatostatin receptors (SSTR) such as Medullary Thyroid Carcinoma, Neuroblastoma, Pheochromocytoma), and others that cannot be accurately studied with Somatostatin SSTR scans such as the OctreoScan (Somatostatin Receptor Scintigraphy (SRS)), which uses the ligand 111In-DPTA-D-Phe-1-octreotide or the newer 68Ga DOTA-peptides.

I-MIBG

Radioiodinated (123I) metaiodobenzylguanidine (MIBG) is an analog of norepinephrine that is used to image catecholamine-secreting NETs such as pheochromocytomas, paragangliomas and glomus tumors. It can also be used to look for Neuroblastoma in children. In patients with functional pheochromocytomas or paragangliomas, this modality has a sensitivity of 90% and positive predictive value of 100%. However, it has limited use in Gastrointestinal (GI) NETs, as this modality was positive in only 49.1% of patients. In the same cohort of patients, OctreoScan was positive in 91.2%. As an imaging tool, this study is best used to confirm a diagnosis of pheochromocytoma or paraganglioma and define the extent of metastatic disease in these tumors. (Note – the Ga68 PET is rising in prominence though). Its most practical use in GI NETs may be to determine whether patients with metastases may benefit from treatment with 131I-MIBG (a form of radiotherapy).

Somatostatin receptor-based imaging techniques

Graphic courtesy of Advanced Accelerator Applications

Somatostatin is an endogenous peptide that is secreted by neuroendocrine cells, activated immune cells and inflammatory cells. It affects its antiproliferative and antisecretory functions by binding to one of five types of somatostatin receptors (SSTR1- SSTR5). These are G-protein coupled receptors and are normally distributed in the brain, pituitary, pancreas, thyroid, spleen, kidney, gastrointestinal tract, vasculature, peripheral nervous system and on immune cells. Expression of SSTRs is highest on well-differentiated NETs. Somatostatin receptor type 2 is the most highly expressed subtype, followed by SSTRs 1 and 5, SSTR3 and SSTR4.

It must be noted that even the most modern scans are not an exact science. Radionuclide scans are like conventional imaging, they can be subject to physiological uptake or false positives, i.e. they can indicate suspicious looking ‘glows’ which mimic tumours. This article explains it better than I can – click here.

The ubiquity of SSTRs on NET cell surfaces makes them ideal targets for treatment (e.g. Somatostatin Analogues (Octreotide/Lanreotide) and PRRT), but also for imaging. There are two primary types of somatostatin receptor-based imaging available:

Octreoscan – In111 based

The most common (currently) is the OctreoScan or Somatostatin Receptor Scintigraphy (SRS), which uses the ligand 111In-DPTA-D-Phe-1-octreotide and binds primarily to SSTR2 and SSTR5. In its original form, it provided a planar, full body image. In modern practice, this image is fused with single photon emission computed tomography (SPECT) and CT. This takes advantage of the specificity of the OctreoScan and the anatomic detail provided by SPECT/CT, improving OctreoScan’s diagnostic accuracy. These improvements have been shown to alter the management in approximately 15% of cases, compared with just OctreoScan images. In primary tumors, the OctreoScan’s sensitivity ranges from 35 to 80%, with its performance for unknown primary tumors dipping beneath the lower end of that range (24%). Its ability to detect the primary is limited by the size but not SSTR2 expression, as tumors less than 2 cm are significantly more likely not to localize but do not have significantly different SSTR2 expression than their larger counterparts.

Octreoscan – Tc99m based

In one study, it was shown that sensitivity and negative predictive
values of Tc-99m-Octreotide scan is significantly higher than that of CT
and MRI. Using Tc-99m instead of In-111 had several advantages that
include better availability, cheaper and higher quality images. In
addition, to less radiation exposure to both patients and nuclear
medicine personnel. In the absence of Ga68 PET, this could prove a reliable alternative. Please note this scan is completed in a single day vs In111 Octreotide time of 2-3 days.

Ga68 PET (or SSTR PET in general)

The newest somatostatin receptor-based imaging modality, although it has been around for some time, particularly in Europe. The most common of these labeled analogs are 68Ga-DOTATOC, 68Ga-DOTANOC and 68Ga-DOTATATE. They may be known collectively as ‘SSTR-PET’. Additionally, the DOTATATE version may often be referred to as NETSPOT in USA but technically that is just the commercial name for the radionuclide mix.

These peptides are easier and cheaper to synthesize than standard octreotide-analog based ligands, boast single time point image acquisition compared to 2 or 3 days with Octreoscan. Its superior spatial resolution derives from the fact that it measures the radiation from two photons coincidentally. SPECT, in comparison, measures the gamma radiation emitted from one photon directly. This results in different limitations of detection – millimeters for 68Ga-PET compared with 1 cm or more for SPECT. There are a few choices of ligands with this type of imaging, but the differences lie primarily in their SSTR affinities – all of the ligands bind with great affinity to SSTR2 and SSTR5. 68Ga-DOTANOC also binds to SSTR3. Despite these differences, no single 68Ga ligand has stood out as the clear choice for use in NETs. As with standard somatostatin receptor-based imaging, these 68Ga-PET studies are fused with CT to improve anatomic localization.

Comparison studies between 68Ga-PET and standard imaging techniques (CT, OctreoScan) have universally demonstrated the superiority of 68Ga-PET in detection of NET primary tumors and metastases. Two early studies compared 68Ga-DOTATOC to standard somatostatin imaging (SRS)-SPECT and CT. Buchmann et al. reported that 68Ga-DOTATOC detected more than 279 NET lesions in 27 patients with histologically proven NETs, whereas SRS-SPECT detected only 157. The greatest number of lesions were detected in the liver. 68Ga-DOTATOC found more than 152 hepatic lesions, while SRS-SPECT found only 105, resulting in a 66% concordance rate between the two modalities. The concordance for abdominal lymph nodes was worse at 40.1%. Cleary these advantages are going to impact on treatment plans, some needing to be altered. In addition, 68Ga-DOTA PET imaging can be used to determine which patients might benefit from use of Somatostatin Analogues (Octreotide/Lanreotide) and PRRT – you can read more about this integrated and potentially personalised treatment in my article on ‘Theranostics‘ – click here.

It’s worth pointing out that SSTR PET is replacing previous types of radionuclide scans, mainly Octreoscan (Indium 111) and is not replacing conventional imaging (CI) such as CT and MRI etc. Whilst SSTR-PET has demonstrated better sensitivity and specificity than CI and In-111, there are specific instances in which SSTR-PET is clearly preferred: at initial diagnosis, when selecting patients for PRRT, and for localization of unknown primaries. For patients in which the tumor is readily seen on CI, SSTR-PET is not needed for routine monitoring. The Journal of Nuclear Medicine has just published “Appropriate Use Criteria for Somatostatin Receptor PETImaging in Neuroendocrine Tumors” which gives guidance on it’s use – issued by the Society of Nuclear Medicine and Molecular Imaging (SNMMI).

Parathyroid Scan – Sestamibi

Sestamibi scanning is the preferred way in which to localize diseased parathyroid glands prior to an operation. This parathyroid scan was invented in the early 1990’s and now is widely available. Sestamibi is a small protein which is labeled with the radio-pharmaceutical technetium99 (Tc99m). This very mild and safe radioactive agent is injected into the veins of a patient with hyperparathyroidism (parathyroid disease) and is absorbed by the overactive parathyroid gland. Since normal parathyroid glands are inactive when there is high calcium in the bloodstream, they do not take up the radioactive particles. When a gamma camera is placed over the patient’s neck an accurate picture will show the overactive gland. Only the overactive parathyroid gland shows up…a very accurate test.

The Sestamibi scan will display the hyperactive gland which is causing hyperparathyroidism in about 90 percent (90% sensitivity) of all patients. If the Sestamibi does show the hyperactive gland it is almost always correct (98-100% specificity). It takes approximately two hours to perform the Sestamibi scan after it has been injected. Pictures of the neck and chest are usually taken immediately after the injection and again in 1.75 to 2.0 hours (shown above). Newer techniques allow for more complete two and three dimensional images to be obtained of a patient’s neck. This technique is called SPECT scanning (Single Proton Emission Computerized Tomography) but it is usually not necessary.

Taking the camera inside and directly to the Tumour

Of course there are other ways to “see it” via several types of Endoscopy procedures – taking the camera to the tumour. Read my article about this by clicking here

A look to the future of PET Scans

Just imagine something which is 40 times better than current PET scan technology? That’s what the scientists are working on now. Here’s an example called “EXPLORER“. Clearly there are more answers required in order to see if this is suitable for use with NETs (i.e. will it work with our radionuclide tracers etc) but it is very exciting and like something out of Star Trek. A little bit of me is worried about ‘overdiagnosis’ so interpretation of something that detailed will be very important to avoid unnecessary worry. Read more here and there is a later update here. Check out this cool video of the 3D images:

Please Share this post

Please Share this post for Neuroendocrine Cancer awareness and to help another patient

Scanning is a key diagnostic and surveillance tool for any cancer. Even though you have elevated bloods or urine (….or not), a picture of your insides is really like a thousand words…. and each picture has a story behind it. Scanning can be a game changer in the hunt for tumours and although scans can’t (yet) confirm the cancer type and grade, they certainly help with that piece of detective work and are key in the staging of the cancer.

When I read stories of people in a difficult diagnosis, I always find myself saying ‘a scan might resolve this’ and I always suggest people should try to get one. Even in the case of a story about late diagnosis or a misdiagnosis, I find myself thinking ‘if only they had done a scan earlier’. Despite what you read on NET forums, a CT scan will normally find some evidence of most tumour activity.

However, scans are not an exact science…..not yet! Apart from human error, sometimes tumours are too small to see and/or there are issues with ‘pickup’ (i.e. with NETs, nuclear scans need efficient somatostatin receptors). However, technology is improving all the time and you can read about this in my blog Neuroendocrine Cancer – Exciting times Ahead.

As for my own experience, I was very lucky. I managed to get a referral to a specialist early on in my diagnosis phase. He looked at the referral notes and said “what are you doing this afternoon”. I replied “whatever you want me to do”. He wanted to scan me. He didn’t know I had cancer but his instincts led him to believe he needed to see inside my body. The scan results were pretty clear – I had a metastatic Cancer and further checks were now needed to ascertain exactly what it was. So I took my seat on the rollercoaster. Here’s something I always say I believe is so much better than the impractical early diagnosis messages that seem to pervade our community: If your doctors don’t suspect something, they won’t detect anything and I believe this is a very frequent outcome of many diagnoses for many cancers (not just NETs).

There’s frequent discussion about the best types of scans for different types of NETs and even for different parts of the anatomy. This is correct and there’s also different views on the subject (including in the medical community), However, a few well known facts that can be gleaned from authortative NET sources. I found this useful video summary from the NET Patient Foundation describing the different scans for NET Cancer and what to expect. Worth a look.

Sooner we can all get access to the latest radionuclide scans the better!